The present invention relates to antennas, and more particularly to frequency selective antennas generally of the parabolic form and used at high frequencies.
Various forms of antennas have been developed and used for many years. Numerous examples of the construction and use of antennas are given in The ARRL Antenna Book published by the American Radio Relay League, Inc., copyrighted in 1974. While antennas vary from a simple wire to complex Yagis, parabolic dishes and the like, a commonly used antenna presently for the reception of high frequency signals is the parabolic dish because of its high-gain characteristic. They are broadband antennas, although the feed horn can be designed to be reasonably frequency selective, and the efficiency of parabolic antennas does not change significantly with size. However, these antennas tend to be large and bulky, heavy, difficult to construct, have large wind-loading surfaces, are unsightly, and are expensive to manufacture.
On the other hand, the present invention provides a high gain antenna that overcomes most of the disadvantages of a parabolic antenna and is an antenna which is highly frequency selective. It is frequency selective to a frequency or small band of frequencies at or near the design wavelength and multiples thereof, and completely cancels signals at one-half the design wavelength and odd multiples thereof. An antenna of the present invention can be manufactured at relatively low cost, and is useful for microwave, radar, satellite and the like communications and reception, and for multipoint distribution systems for television and relay paths, including optical reflection, and other uses where select frequencies need to be reinforced through in-phase gathering at a focal point.
An antenna constructed in accordance with the teachings of the present invention comprises a plurality of parabolic segments each having a different parabolic surface related to the frequency involved, and each offset axially from the next. The antenna is relatively thin or has a narrow or low profile. This significantly reduces wind-loading factors and provides a more aesthetically and environmentally pleasing, or less obtrusive, antenna particularly for use in direct reception of satellite television signals such as by individuals in residential areas. If used, for example, on the roof of a residence this antenna would be significantly less obtrusive than a parabolic dish designed to receive signals of a similar frequency. The antenna is relatively simple to construct, and its form can be modified readily for the reception of a different frequency or narrow frequency band. The antenna can be constructed of various materials and be manufactured using numerous conventional techniques.